The present invention relates to improvements in corrugated paperboard manufacture. Typically such corrugated paperboard is manufactured rom two or more liners and fluted medium. To produce a double-lined single wall corrugated board, a single-face liner and a double-face liner are used. The fluted medium is produced and glued to the single-face liner to form the single-face web. This web is then glued to the double-face liner to form the corrugated board. In cases where a plastic film or wax coating is desired on one face of the corrugated board, it is taken from the corrugator in sheets and processed as sheets through a device in which the plastic film is adhesively laminated or adhered onto the board, or the board is passed through a roller coater in which a layer of wax in liquid form is flowed over and roller-coated onto the corrugated board as is desired. These off-line coatings of film or wax have been used to enhance the barrier properties of the corrugated board. Extrusion laminated polyethylene structures have been made before in which the plastic is buried between two layers of kraft paper. In other cases, packages made of corrugated board have used separate polyethylene plastic bags enclosing them to provide product protection. The off-line extrusion or coating methods have not been economical or practical for commercial production.
In the production of corrugated paper, the heat of drying the adhesive involves contacting the paper with preheat drums, hot plates and the like which operate at temperatures on the order of 350.degree. F. This exceeds the softening point of plastics, such as polyethylene, and the extrusion coating and adhering of the plastic with the liner paper results in softening the plastic and a subsequent transfer of the plastic material to the drums and hot plates of the corrugator equipment results, which is unacceptable for continued production.